The present invention relates to a probe for use in a nuclear magnetic resonance (NMR) apparatus and the nuclear magnetic resonance apparatus equipped with the probe.
The nuclear magnetic resonance (NMR) apparatus irradiates a sample which is placed in a static magnetic field formed by a magnet with a high frequency electromagnetic wave, and detects a nuclear magnetic resonance signal emitted by the sample. The nuclear magnetic resonance apparatus is considered to be appropriate for the analysis of molecular structures. In the nuclear magnetic resonance apparatus, a probe coil has both a role for irradiating the sample with a high frequency magnetic field and a role for detecting the signal emitted by the sample. The irradiation is performed by a transmission coil, and the detection is performed by a receiving coil. A single coil may be used to perform both the transmission and reception. Alternatively, they may be performed by separate coils. In both cases, it is desirable that the magnetic field produced by the transmission coil is uniform in the region surrounding the sample during irradiation, and that the receiving coil is capable of efficiently receiving a signal during detection.
When a single coil plays both roles for transmission and reception, one tuning and matching circuit is required for one transmission/receiving coil. Tow or more capacitors for adjusting resonance frequency and for matching impedance are disposed in the tuning and mating circuit. Since one coil is provided, one set of the circuits for performing matching is sufficient. However, an additional switching circuit is needed for switching the connection to a transmitter and to a receiver. A method of performing the transmission and reception with a single coil through the use of such a switching circuit is described in JP-A-2002-207072 (Claims).
In contrast, when separate coils are used to perform the transmission and reception (irradiation and detection), two coils for transmission and reception are provided respectively. Therefore, two sets of tuning and matching circuits are required. This method enables the shape of each coil to be optimized independently, thus providing advantages over the single coil in various ways. For example, a coil that employs a superconductor reduces resistance, thus being able to enhance a Q (Quality-factor) value of resonance and thereby to improve sensitivity. However, in the type having separate coils for transmission and reception respectively, there arises a problem that signal detection sensitivity of the receiving coil is deteriorated due to an electromagnetic coupling between the two coils. Conventionally, such a problem has been solved by precisely disposing the coils in such a way that magnetic fields generated by each coil are perpendicular with each other, or by reducing a coupling that slightly remains through fine-tuning of the relative positions of the coils in a trial and error manner.